WASHINGTON, March 6 (Reuters) - A spectacular array of beautifully preserved fossils unearthed in northeastern China over the past two decades provides a unique portal on life 160 million years ago in the Jurassic Period, an international team of scientists said this week.

Among them are outlandish feathered dinosaurs, a quirky flying reptile, the earliest known gliding mammal, the earliest known swimming mammal - and a salamander that turned up everywhere.

Writing in the Journal of Vertebrate Paleontology, they said the plant and animal fossils collectively represent a distinct ecological grouping - or biota - of life forms that existed alongside one another.

The fossil record of life on Earth is notoriously spotty, with some spans of time remaining all but unknown. That is not the case in what these scientists call the Daohugou Biota, named for a village in the region the fossils have been found.

"It is an unprecedentedly good window into that particular place and time," paleontologist Corwin Sullivan of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, who led the research, said in a telephone interview on Thursday.

"It is a time when a lot of interesting things are happening," paleontologist David Hone of Queen Mary University of London added in a telephone interview. "We've got feathered dinosaurs. We've got weird mammals. We've got fish. We've got lizards. We've got all this wonderful, wonderful stuff."

The fossils have been found in western Liaoning Province and nearby areas. It was an inland region filled with trees, dotted with lakes and teeming with life 160 million years ago.

The level of preservation has been exceptional, with only a handful of other places in the world offering fossils as good.

SOFT TISSUE

Scientists count themselves lucky if even the hard parts of an animal like bones and teeth become fossils. In the Daohugou Biota, many show soft tissue including feathers, fur, skin and, in some of salamanders, even delicate external gills.

The Jurassic is the second of three time periods that make up the Mesozoic Era, sometimes called the Age of Dinosaurs. The Triassic preceded it and the Cretaceous followed it.

The animals and plants of the Daohugou Biota were found in the same part of China as a group of similarly amazing fossils that are 30 million years younger, from the Cretaceous. Those later remains - including primitive birds and more feathered dinosaurs - comprise what is called the Jehol Biota.

The Daohugou Biota includes the earliest dinosaurs preserved with feathers. Some, like Epidendrosaurus and Epidexipteryx, are remarkably bird-like.

Scientists say birds evolved from small, feathered meat-eating dinosaurs. The earliest known bird is Archaeopteryx, from 150 million years ago. Scientists are eager to find even earlier birds and think this might be an ideal place to look.

"You've got a bunch of very bird-like dinosaurs. We do not yet have a definitive bird there," Hone said. "It's the best possible place we have got anywhere to find a true bird older than Archaeopteryx. That will be the place."

One of the ways the scientists were able to determine that fossils from the Daohugou Biota belonged together was that one particular salamander called Chunerpeton kept popping up, indicating the varied remains represented one place and time.

The scientists said a pterosaur - flying reptile - called Darwinopterus is considered a "transitional" form. It possessed features of more primitive pterosaurs like a long tail and those of later, more advanced ones like a big head.

The mammal Volaticotherium boasted a membrane between its arms and legs that enabled it to glide from trees. It was the Jurassic equivalent of a flying squirrel - except that today's flying squirrels do not have to steer clear of dinosaurs.

Another mammal, Castorocauda, was semi-aquatic and looked a bit like a beaver. It had a broad scaly tail - like a beaver's - and webbed feet for swimming but belonged to a completely different and now extinct group of mammals.

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